Butterfly valves are employed in pipelines and other piping applications to control the flow of liquids through the piping. In a typical application, the butterfly valve comprises a round, disk-shaped valve member which is mounted on a valve stem. The valve stem is rotated to position the valve member either perpendicularly to the flow of liquid through the piping thereby closing the valve, or parallel to the flow of liquid through the piping thereby opening the valve. The valve stem is rotated either manually or by means of a suitable actuator.
From time to time it is necessary to remove the valve stem actuation apparatus for maintenance and repair. When the valve stem actuation apparatus is returned to service, it is frequently impossible to determine the exact positioning of the valve member with respect to its fully opened and fully closed positions. This in turn leads to difficulty in determining with certainty when the valve member is in its fully closed position.
The present invention comprises a position sensing system which is particularly adapted for use with butterfly valves. By means of the invention, the precise positioning of the valve member of a butterfly valve with respect to its fully opened, partially opened, partially closed, and fully closed positions can be determined at any time.
The position sensing system of the present invention comprises a washer secured to the lower end of the valve stem of a butterfly valve. At least one magnet is mounted on the washer for rotation with the valve stem and the valve member mounted thereon. A sensor is mounted beneath the washer for actuation by the magnet. Upon actuation of the sensor, a signal indicative of the positioning of the valve member is generated.